The inventor has developed the sewage sludge incinerator shown in FIG. 1 and further the sewage sludge incinerator provided with sewage sludge heater B given in FIG. 2.
This invention relates to an evaporative concentrator for sewage sludge to be used for a sewage sludge incinerator instead of the sewage sludge heater B illustrated in FIG. 2 in order to improve the sewage sludge incinerators above in performance as follows: This invention relates to an evaporative concentrator for sewage sludge effective when sewage sludge with comparatively low calorific value such as that with water content rate 80 percent or more, or dried sewage sludge with heating value 3500 kcal/kg or less is incinerated.
This invention also relates to an evaporative concentrator for sewage sludge to be used with a sewage sludge incinerator, instead of the sewage sludge heater B given in FIG. 2. Before the description of this invention, the sewage sludge incinerator in FIG. 1 and the sewage sludge incinerator provided with the sewage sludge heater in FIG. 2 are first described.
The sewage sludge incinerator given in FIG. 1 is for sewage sludge with comparatively low water content rate, involves sewage sludge with water content from 60 to 70% therein, and the sewage sludge in hopper A is fed to drying furnace C having a fluidized sand bed by compulsory supply means 1, such as a screw feeder, mounted on the bottom of the said hopper A. A required high pressure gas rate at a temperature as high as 200.degree. to 400.degree. C. is fed from the bottom space of sand layer into drying furnace C through supply pipe 3, the sand layer is fluidized with this gas for drying; the sewage sludge fed is pulverized and dried with the sand fluidized. The yielded product by the said drying furnace C is sucked through discharge pipe 4 having blower 8, is taken out of the said drying furnace from the top thereof, is separated to the solid and the gas by a separation means such as cyclone separators 5 and 5', the solid is contained in hopper 6 therebeneath, and is fed to combustion furnace D by powder supply means 7 thereunder at approximately constant quantity per hour. FIG. 1 shows the two-stage combustion system consisting of incomplete combustion furnace D.sub.1 and complete combustion furnace D.sub.2. The air for combustion is sent by blower 9, is first preheated through air preheater 10 installed around the periphery of complete combustion furnace D.sub.2, then is divided into two suitable quantities, and is supplied to incomplete combustion furnace D.sub.1 through branch pipe 11 and to complete combustion furnace D.sub.2 through branch pipe 12 respectively. The product of the complete combustion furnace D.sub.2 is taken out thereof through exhaust gas pipe 15 having blower 13, is lowered in temperature through heat exchanger E and is discharged after the ash content is separated through filter 14.
The gas separated by separation means 5 flows through circular piping 16, which is the exhaust pipe of blower 8, however, a part of the gas is fed to incomplete combustion furnace D.sub.1 by providing branch pipe 21 on the said circular piping 16, and another part of the gas is supplied to complete combustion furnace D.sub.2 by further providing branch pipe 22 on the said same piping 16. The residual gas is carried through circular piping 16, is heated by heat exchanger E and is supplied again to drying furnace C having the fluidized sand bed through feed pipe 3 as drying gas.
Gas rate Q.sub.1 kg/h sent to the said drying furnace for drying is a rate required for allowing sewage sludge rate M kg/h supplied to the said drying furnace to be heated from room temperature up to about 120.degree. C. and to evaporate the water content thereof, and the said gas rate Q.sub.1 kg/h will circulate in circular piping 16. Further, Q.sub.2 kg/h, the total gas rate supplied to incomplete and complete combustion furnaces D.sub.1 and D.sub.2 showed be approximately equal with the gas rate generated from sewage sludge rate M kg/h fed to drying furnace C. The sewage sludge incinerator having the sewage sludge heater in FIG. 2 is a suitable apparatus for incinerating sewage sludge with water content rate about 80 percent or that with dried heating value, 3500 kcal/kg or less. In FIG. 2, sewage heater B is installed between compulsory supply means 1 mounted under the bottom of hopper A containing sewage sludge and drying furnace C having the fluidized sand bed. Sewage sludge is heated near 100.degree. C. by the said heater B and is fed into drying furnace C having the fluidized sand bed; thus, sewage can more easily be dried in the said drying furnace C than before. The dried sewage sludge product yielded in the said drying furnace C is divided into the solid and the gas by separation means 5, the solid is contained in hopper 6 below, and is fed to incomplete combustion furnace D.sub.1 by powder supply means 7 at approximately constant rate per hour. The gas divided by separation means 5 is pressurized by blower 8, passes the circular piping 16, is heated by heat exchanger E, and then required rate Q'.sub.1 kg/h thereof is supplied to drying furnace C as drying gas. The remaining gas rate Q'.sub.2 kg/h is fed to the said sewage sludge heater B through supply pipe 17 as heating gas. The gas lowered in temperature as a result of the heat exchange in the said sewage sludge heater B is taken out through pipe 18, the drain is removed by drain separation means 19. The removed drain is taken out of the system, and the gas from which the drain is removed is fed to incomplete combustion furnace D.sub.1 through supply pipe 20.
As such, the sewage sludge incinerator having sewage sludge heater B as given in FIG. 2 is not only to be able to dry sewage sludge easily, because the sewage sludge heated near 100.degree. C. in temperature, consequently, sewage sludge extremely lowered in viscosity is fed to drying furnace C, but also gas allowed to reduce the water content is fed to combustion furnaces D.sub.1 and D.sub.2 ; thus, the primary incomplete and the secondary complete combustions can smoothly be performed.